Transverse radiator device for heating non-metallic materials in an electromagnetic radiation field



Feb. 10, 1970 H. A. PUSCHNER 3,495,062

TRANsvERsE RADIATOR DEVICE FOR HEATING NON-METALLIC MATERIALS IN AN ELECTROMAGNETIC RADIATION FIELD Filed June 10, 1966 2 Sheets-Sheet 1 Figf E b 19.2 4 a 7 IN VE NT 0R 9%: dzmm Feb. 10, 1970 H. A.'PUSCH'NER 3,495,062

TRANSVERSE RADIATOR DEVICE FOR HEATING NON-METALLIC MATERIALS IN AN ELECTROMAGNETIC RADIATION FIELD Filed June 10, 1966 2. Sheets-Sheet 2 Fig.4

I3 IN VE N TOR United States Patent 3,495,062 TRANSVERSE RADIATOR DEVICE FOR HEATING NON-METALLIC MATERIALS IN AN ELECTRO- MAGNETIC RADIATION FIELD Herbert Auglst Piischner, Osterholzer Heerstrasse 175, Bremen, Germany Filed June 10, 1966, Ser. No. 556,735 Claims priority, application Germany, June 18, 1965, A 49,508 Int. Cl. Hb 9/06 US. Cl. 219-1055 9 Claims ABSTRACT OF THE DISCLOSURE A stacked array of rectangular waveguides open at one end and short-circuited at the other are excited with an H wave from a coaxial transmission line through a loop coupling passing from the inner conductor of the transmission line through openings in the outer conductor and the short circuiting plate of each rectangular waveguide. Material to be heated is passed across the plane embracing the open ends of the rectangular waveguides to provide a system for uniformly and efficiently heating the material over a wide range of microwave frequencies.

The invention relates to a transverse radiator device for heating non-metallic materials in an electromagnetic radiation field, more particularly for microwave continuous throughput installations.

A segment antenna has been proposed, having a rectilinear excitation element and two secondary radiators arranged symmetrically to the axis of the antenna. The amplitude distribution at the aperture along the broad side of the antenna fluctuates very considerably and as a result of this the antenna is unsuitable for use in uniform heating of material by the radiation. Moreover, the large structural height of the antenna is disadvantageous. A parabolic horn has been proposed, the amplitude variation of the radiation of which extends approximately sinusoidally over the aperture. As a result of this, it is unsuitable for use as a radiator for installations having a large throughput width. Both radiators have considerable disadvantages with regard to requirements of broad band width and tolerance to mismatching under conditions of highly fluctuating loading by the material passing by, this being connected with large fluctuations of the radiation wave amplitude in dependence on frequency.

It is an object of the invention to provide a transverse radiator device which has a relatively homogeneous wave amplitude distribution over the aperture.

According to the invention the transverse radiator device comprises a group of discrete radiator elements in the form of short circuited E-sector horns the dimension of which in the Wave propagation direction is smaller than two wavelengths in free space, and which are arranged for being excited into H oscillation, the horns being ararnged in a row with their broad sides extending perpendicularly to the polarisation direction, the polarisation direction in the aperture of all horns being the same. Accordingly, in longitudinal direction of the transverse radiator device, a homogeneous amplitude distribution is achieved, so that the material which moves past the aperture perpendicularly to the longitudinal direction of the radiators is uniformly heated. For feeding the individual radiator elements, a wave guide, preferably a coaxial line, may be provided, which has coupling openings at periodic spacings, preferably at half wavelength intervals of the wave guide, to which the radiator elements are coupled in known manner. Coupling loops of the radiator elements, which excite the rectangular wave guide or the E-sector born into H oscillation can extend through these openings into the coaxial line and can be capacitively or conductively coupled there by known means.

In addition to the advantage of uniform energy distribution in the longitudinal direction of the transverse radiator, mentioned above, the transverse radiator has a series of other advantages compared with known radiators. The wave amplitude course has a considerably lower frequency dependence, so that it satisfies an important requirement, namely that generators with any frequency lying within a predetermined frequency band can be connected, without the energy distribution fluctuating essentially.

The matching of the transverse radiator to loading conditions, imposed by the material, fluctuating considerably, is very much better than with known radiators. As a further advantage, any desired radiator length can be produced by adding further radiator elements on the building block principle. Furthermore, the structural height of the radiator device of the invention is small. The generator can be directly connected with the feed line, and simple compensation can be achieved with compensation means.

In order to make the invention clearly understood, reference will now be made to the accompanying drawings which are given by way of example and in which:

FIG. 1 is a perspective view of a conventional E-sector horn;

FIG. 2 shows the wave amplitude course for the aperture of the horn of FIG. 1, with vertical polarisation;

FIG. 3 is a perspective view of an embodiment of the transverse radiator according to the invention;

FIG. 4 shows the wave amplitude course for the aperture of the radiator of FIG. 3, with vertical polarisation of the radiator elements;

FIG. 5 is a longitudinal section of the transverse radiator of FIG. 3; and

FIG. 6 is a fragmentary sectional view of the coupling system of the radiator of FIG. 5.

In FIG. 1, a conventional E-sector horn 1 is illustrated which is excited from a coupling opening 2 by a coupling loop 3. If this horn is excited with an H wave 4, then the amplitude distribution 5, 6, is produced, which is indicated by the shaded surfaces in FIG. 2, for the aperture 7 with the rectangular sides a and b of this E-sector horn 1. In the vertical plane 5 the distribution is homogeneous and in the horizontal plane 6 the distribution is sinusoidal. In FIG. 3, which shows an embodiment of the transverse radiator according to the invention, the serial arrangement of a plurality of E-sector horns (or open rectangular hollow guides) 8, 9, 10, 11, 12 and the excitation from a coaxial feed line 13 by known coupling elements 14, 15 is illustrated. The coupling loops in successive radiator elements are displaced through relative to each other in order that the polarisation of all radiator elements has the same direction. If the individual radiator elements 8 to 12 are excited in the same phase by. coupling elements 14, 15 having the abovementioned 180 displacement, then an amplitude distribution 16, 17, is given as shown in FIG. 4, for the aperture 18 having the rectangular sides a and b, this being indicated by the shaded surfaces.

In FIG. 5, the construction of the transverse radiator and the generator 19 connected therewith, with the compensation line 20 disposed therebetween can be seen. A part of the wave coming from the generator is coupled from the coupling pin 21 into the E-sector horn 22, which is excited into H oscillation by the inductive loop 23. The radiation wave is transferred from the aperture 18 to the goods 24 being heated. The remaining part of the wave is further propagated to the next coupling opening 25, where again a part of the wave is coupled out, the coupling loop 26 in the E-sector horn 27 being displaced through 180 relative to the first coupling 23. The coaxial line is terminated with a short circuit 28, which is spaced by one quarter or one half wavelength from the last coupling opening 29. The coupling is so adjusted that the amplitude distribution 16, 17 over the aperture 18 of the transverse radiator is homogeneous. The necessary penetration depth of the coupling pin 21 into the coaxial line 13 can be adjusted by the screw connection 30 illustrated in FIG. 6.

The coaxial line has the same cross section as the output coupling of the microwave generator 19' connected thereto. For compensation of mismatching of the transverse radiator, known compensation means, for example pins or plates, are provided between the generator and the transverse radiator.

I claim:

1. Microwave heating apparatus comprising,

means defining a contiguous array of hollow conducting waveguides dimensioned to propagate the H mode between an input surface and an output surface separated from the output surface by a distance that is less than two wavelengths of exciting microwave energy in air,

said waveguides being open at said output surface,

conducting means in said input surface for short circuiting said conducting waveguides at said input surface, an input waveguide adjacent to said input surface for carrying said exciting microwave heating energy,

means for coupling said exciting microwave heating energy from said input waveguide through said conducting means to each of said hollow conducting waveguides for cophasally and codirectionally exciting the mouths of each of the latter waveguides with said exciting microwave heating energy,

and means for establishing relative movement between dissipative material adjacent to said output surface and said mouths in a direction across the latter for heating said material with said exciting microwave energy.

2. Microwave heating apparatus in accordance with claim 1 wherein said input and output surfaces are parallel planes.

3. Microwave heating apparatus in accordance with claim 2 wherein said hollow conducting waveguides are rectangular.

4. Microwave heating apparatus in accordance with claim 2 wherein said hollow conducting waveguides are square.

5. Microwave heating apparatus in accordance with claim 1 wherein said input waveguide is a coaxial transmission line having its outer conductor adjacent to said input surface.

6. Microwave heating apparatus in accordance with claim 5 wherein said means for coupling comprises coupling loops including a conducting link extending from the coaxial transmission line inner conductor to a conducting wall common to a contiguous waveguide whereby alternate common conducting walls have two of such conducting links while the remaining common conducting walls have none to thereby cophasally and codirectionally excite the mouths of each hollow conducting waveguide with said exciting microwave heating energy.

7. Apparatus for heating non-metallic materials in an electromagnet radiation field comprising,

a plurality of side-by-side waveguide radiators having individual open ends which together form a common elongated aperture, common feed waveguide coupled to said plurality of waveguides for coupling energy to said plurality of waveguides through coupling holes in each, said common feed waveguide being arranged for establishing standing wave conditions, said coupling holes being spaced substantially a half wavelength apart in said common feed waveguide,

and means for establishing a phase reversal between energy coupled through adjacent ones of said coupling holes.

8. Apparatus in accordance with claim 7 and further comprising short circuiting means for establishing said standing wave conditions.

9. Apparatus in accordance with claim 7 and further comprising a corresponding plurality of coupling loops extending through said coupling holes into said common feed waveguide for establishing reactive coupling between said common feed waveguide and each of said plurality of waveguides whereby coupling loops of an adjacent r pair of said plurality of waveguides are relatively displaced by substantially References Cited UNITED STATES PATENTS 2,689,303 9/1954 Risser 343-771 XR 2,903,695 9/ 1959 Jamieson 343-853 XR 3,263,052 7/1966 Jeppson et a1. 219'-10.55 2,349,942 5/1944 Dallenbach 343776 2,398,095 4/ 1946 Katzin 343786- XR 2,628,311 2/ 1953 (Lindenblad 343786 XR 2,718,592 9/1955 Smith 34-3-786 XR 2,908,002 10/1959 Van Atta 343-776 HERMAN KARL SAALBACH, Primary Examiner MARVIN NUSSBAUM, Assistant Examiner U.S. Cl. X.R. 

